I have a ford mondeo TDCI and it is making big clouds of black smoke when accelerating and starts chugging when going an average speed! Had car serviced and EGR valve cleaned but with no joy! Anybody had this problem and can anyone help? Thanks

Got a ford mondeo 2ltr TDCI which is now producing black smoke upon acceleration and when at an average speed keep chugging as though it wants to stall! I have had it serviced with no change also had the EGR valve cleaned and had all the maintained kits through the car with no change! Need help as to what it could possibly be? Hoping someone has had this same problem and its not just me Thank you